Grease a 13” x 18” rimmed baking sheet generously with olive oil, including the sides, and set aside.

Whisk together flour, instant yeast, baking powder, 1 tablespoon rosemary, and salt in a large bowl. In a smaller bowl combine warm water, ½ cup olive oil, and apple cider vinegar. Pour into dry mix and mix with a large spoon until well mixed. It will be quite wet and sticky. Use a rubber spatula to pour/scrape mixture into the greased pan, spreading it flat all the way to the edges. Loosely cover with plastic wrap and let sit in a warm spot for 40-50 minutes to rest and rise a bit.

Preheat oven to 400 degrees F.

In a small sauté pan, sauté the sliced onion with 1 tablespoon of olive oil over medium/low heat for a few minutes, until translucent but not starting to brown. Remove from heat and set aside.

After the resting time is up for the dough, pour another 2 tablespoons of olive oil over the top of the dough, spread it around with your hand, and then make shallow dimples all over the surface with your fingertips. Press the olive halves into the dimples, evenly spread the softened onions over the top, then sprinkle with the rosemary. Bake for about 20-25 minutes, until golden brown and a toothpick comes clean from the middle. Let cool before cutting and serving.